SHAPE ANISOTROPY OF FERROELECTRIC DOMAINS IN A LANGMUIR MONOLAYER

We determine the shape of ordered domains in a Langmuir monolayer deposited on the surface of water, when the amphiphilic molecules carry electric dipoles oriented in the same direction. The screening of charges by water is taken into account. For horizontal dipoles, one can calculate the anisotropic line energy between the ordered and the disordered phase. The corresponding domains are elongated and, in some cases, look like long sharp needles. The addition of a vertical component to the dipole results in a further elongation of these domains; even for infinitely long needles, the width keeps a finite asymptotic value. These predictions agree with our recent observations on fluorescent nitrobenzoxadiazole (NBD)-stearic acid films.